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**Electron Configuration**

Mapping the electrons

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**Electron Configuration**

The way electrons are arranged around the nucleus.

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**Quantum Mechanical Model**

1920’s-1930’s Werner Heisenberg (Uncertainty Principle) Louis de Broglie (electron has wave properties) Erwin Schrodinger (mathematical equations using probability, quantum numbers)

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**Heisenberg uncertainty principle**

it is impossible to determine simultaneously both the position and velocity of an electron or any other particle with any great degree of accuracy or certainty.

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Erwin Schroedinger Formulated equation that describes behavior and energies of subatomic particles. Incorporates both particle and wave behavior in terms of wave function: is proportional to the probability of finding an electron.

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**Erwin Schroedinger (cont’d)**

Leads to Quantum Mechanics: we cannot pinpoint an electron in an atom but we can define the region where electrons can be in a particular time……. called a “probability map”….a 3-dimensional area in space called an ORBITAL

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**Principal Quantum Number, n**

Indicates main energy levels n = 1, 2, 3, 4… Each main energy level has sub-levels s p d f

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**Orbital Quantum Number, ℓ (Angular Momentum Quantum Number)**

Indicates shape of orbital sublevels ℓ = n-1 ℓ sublevel 0 s 1 p 2 d 3 f 4 g

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**electron’s energy depends principally on this **

Quantum numbers and orbital energies Each electron in an atom has a unique set of quantum numbers to define it { n, l, ml, ms } n = principal quantum number electron’s energy depends principally on this l = azimuthal quantum number for orbitals of same n, l distinguishes different shapes (angular momentum) ml = magnetic quantum number for orbitals of same n & l, ml distinguishes different orientations in space ms = spin quantum number for orbitals of same n, l & ml, ms identifies the two possible spin orientations Unit 6- Atomic Electon Configurations and Periodicity 9

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**Energy level Sublevel # of orbitals/sublevel **

n = 1 1s (l = 0) 1 (ml has one value) n = 2 2s (l = 0) 1 (ml has one value) 2p (l = 1) 3 (ml has three values) n = 3 3s (l = 0) 1 (ml has one value) 3p (l = 1) 3 (ml has three values) 3d (l = 2) 5 (ml has five values) n = principal quantum number (energy) ml = magnetic quantum number (orientation) l = azimuthal quantum number (shape) Unit 6- Atomic Electon Configurations and Periodicity 10

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**Concept: Each electron in an atom has a unique set of quantum numbers to define it { n, l, ml, ms }**

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The principle quantum number, n, determines the number of sublevels within the principle energy level.

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Orbital The space where there is a high probability that it is occupied by a pair of electrons. Orbitals are solutions of Schrodinger’s equations.

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Orbitals

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**Visualizing the orbitals**

s orbitals are spherical p orbitals are “dumbell” shaped d and f are harder to visualize

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**Orbitals in Sublevels Sublevel # Orbitals # electrons s 1 2 p 3 6**

d f

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**Three rules are used to build the electron configuration:**

Aufbau principle Pauli Exclusion Principle Hund’s Rule

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Aufbau Principle Electrons occupy orbitals of lower energy first.

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Orbital Diagram

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Filling Order diagram

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**-Pauli Exclusion Principle (Wolfgang Pauli, Austria, 1900-1958) -Electron Spin Quantum Number**

An orbital can hold only two electrons and they must have opposite spin. Electron Spin Quantum Number (ms): +1/2, -1/2

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Hund’s Rule In a set of orbitals, the electrons will fill the orbitals in a way that would give the maximum number of parallel spins (maximum number of unpaired electrons). Analogy: Students could fill each seat of a school bus, one person at a time, before doubling up.

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**Orbital Diagram for Hydrogen**

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**Orbital Diagram for Helium**

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**Orbital Diagram for Lithium**

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**Orbital Diagram for Beryllium**

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**Orbital Diagram for Boron**

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**Orbital Diagram for Carbon**

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**Orbital Diagram for Nitrogen**

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Orbital Diagram

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**Notations of Electron Configurations**

Standard Shorthand

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**Orbital Diagram for Fluorine**

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**Standard Notation of Fluorine**

Number of electrons in the sub level 2,2,5 1s2 2s2 2p5 Main Energy Level Numbers 1, 2, 2 Sublevels

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Noble Gas Notation Use the last noble gas that is located in the periodic table right before the element. Write the symbol of the noble gas in brackets. Write the remaining configuration after the brackets. Ex: Fluorine: [He] 2s2 2p5

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**Blocks in the Periodic Table**

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